Fig. 1

Scale-fragments deposited in thermal water transport pipes of different depths as well as successively accumulated on heat exchangers of two geothermal power plants. a Steel pipes dismounted from a deep geothermal borehole during a major maintenance procedure in front of the geothermal facility. b Carbonate scale-fragments flaked off from the interior of a steel pipe. c Massive block of cemented carbonate scale-fragments clogging an outer heat exchanger surface within weeks to few months. d Rough growth surface of dark crystalline Mg-calcite scale-fragment precipitated inside a pipe (sample KIR33 collected from a deeper production well section). e View on agglomerated and cemented scale-fragments of variable sizes recovered from a heavily impaired heat exchanger in the power plant